The present invention relates to a plant for preparing over-run edible ice-cream, the plant comprising a completely or partly freezing apparatus for freezing an ice-cream mixture (mix), the freezing apparatus being fed with mix via a feeding conduit by means of a feeding pump, an air mass flow from a source of pressure air being added to the mix between the feeding pump and the freezing apparatus by means of an air supply apparatus, the air supply apparatus being controlled by means of a signal from a computer in such a way that the rate of the air mass flow depends upon the mix flow flowing through the feeding conduit, the mix flow being measured by means of a mix flow meter provided in the feeding conduit and connected with the computer.
A plant of the kind referred to above is disclosed in U.S. Pat. No. 4,747,272. According to this patent the mix flow through the feeding pump is measured by means of a volume flow meter, which delivers a signal directly proportional to the volume flow to the computer, which issues a signal that is directly proportional to the volume flow to the air supply apparatus in such a way that the air supply apparatus delivers an air mass flow to the mix in the feeding conduit that is directly proportional to the mix volume flow through the volume flow meter of the pump.
It should be mentioned that the ice-cream mixture to be used in the production of edible ice-cream, and which is here termed "mix", is mixed with air which is termed "over-run" in order to achieve a porous character of the final ice-cream. In order to freeze the air mixed (over-run) ice-cream mixture (mix) correctly, it is important that the percent over-run is correct, i.e., adjusted in the right way with respect to the composition of the mix and to the conditions prevailing during the freezing. The percent over-run is here defined as the the ratio between the weight of one volume mix (without air) multiplied by 100 and the weight of the same volume ice-cream from which ratio 100 is substracted.
Accordingly, it will be understood that if the mix after the over-run e.g. contains 50 volume percent mix and 50 volume percent air, the over-run is 100 percent and that the percent over-run will increase by increasing air addition and decrease by decreasing air addition.
A mix is prepared by mixing different ingredients known per se, and during such mixing also air will often be introduced into the mix. If the mix fed to the plant contains air and the volume flow rate of the mix is used in order to produce a signal directly proportional thereto for controlling the air supply as the case is according to the prior art referred to above, such air supply will be wrong because the air content in the mix will add to the control signal as if the air in question were mix.
This is unfortunate because a percent over-run which varies with respect to the one requested has a harmful influence upon the final product. This is due to the fact that the freezing apparatus is to be controlled in such a way that a requested viscosity of the product treated in the freezing apparatus is obtained and the parameters to be observed in this connection are in particular the pressure and the exit temperature. These parameters are adjusted according to the viscosity requested and a wrong percent over-run will not give the requested result by using operation parameters adjusted to another predetermined percent over-run. The result such wrong treatment is that the product, when it later on partly or completely melts displays a thin consistency.
It has been tried to improve the consistency of the final product when partly or completely melted partly or completely in connection with a freezing apparatus wherein the operating parameters thereof inclusive the percent over-run is controlled manually, viz. by mixing the mix and the air intimately with each other before the mixture is fed into the freezing apparatus. Thereby it has sometimes been possible to obtain a product having a cream-like consistency when completely or partly melted, but it has not been possible in this way to obtain good results in a reproduceable way. For instance, it has not been possible to achieve a product which always obtains the desired advantageous qualities. Presumably, this is due to the fact that previously it has not been realized that an exact observance of the percent over-run plays an important part for the final result. Moreover, it should in this connection be noticed that the factor used for controlling a manually controlled freezing apparatus is the viscosity of the material leaving the freezing apparatus and a previously determined viscosity may be achieved within a broad range of control both as regards the operating temperature and the pressure in the freezing apparatus, the exit temperature of the product, and the percent over-run, but such parameters must of course be mutually co-ordinated.